Wind power units (“WPUs”) generally employ a number of methods to limit rotor and overall structural loads for the entire set of wind and operating conditions predicted over the WPU operating life at a particular site. Multiple control methods can be used to manage loads during operation, including blade collective pitch, individual blade pitch, and yaw axis control to align the WPU with the prevailing wind inflow direction.
Yaw control systems typically employ one or more wind direction sensors mounted on the nacelle cover behind the rotor, or less commonly on a separate tower assembly mounted on an upwind side of the blade rotor hub. Conventionally, the WPU control system uses yaw error information to operate a yaw control system that typically uses electric or hydraulic motors to rotate the nacelle relative to the tower support. To control required actuation loads and to limit additional loads caused by high yaw rates, WPUs are typically designed with low yaw angular rates.
Because of the low yaw rates, during operation in dynamic wind conditions it is possible to encounter conditions where the WPU is operating at its full rated rotor speed and with a large yaw angle error. As the yaw angle increases, blade and tower top loads significantly in excess of normal operating loads can be introduced. Such a high yaw angle operating load can be a defining critical load for the turbine structural design. There is thus a need for improved control methods and systems to anticipate the onset of such load conditions and invoke a control regime to protect against undesirable load conditions that may otherwise result.